Intestinal Brush Border Membrane Enzyme Activities of Rats Fed Chemically Defined Diets Containing Oligopeptides or Amino Acids as the Nitrogen Source

Abstract

We have investigated the effect of oligopeptides on brush border membrane aminopeptidase and cytosol peptidase activities in rat small intestine. Activities of these enzymes were significantly higher in the group fed a diet containing small peptides (SP group) than in the group fed a diet containing a mixture of amino acids (AA group). There were no significant differences in the activities of maltase, sucrase, lactase, and alkaline phosphatase between the two diet groups. The elevation of activity of brush border membrane aminopeptidase was inhibited by cycloheximide, indicating this enzyme to be an adaptive enzyme induced by oligopeptides as intraluminal substrates. The SP group also showed increased absorption of not only Gly-Leu, the dipeptide, but also of Gly and Leu, the free amino acids. The present study indicates that there could be advantages of using oligopeptides rather than amino acids as the nitrogen source in chemically defined diets from the viewpoint of peptidase activities as well as absorption of amino acids.